Hydraulic pumps and hydraulically driven shafts (motors) respectively as generally described above are known. The plungers are connected to the oblique plate by means of ball joints. On rotation of the shaft the plunger(s) move to and fro and the passages of the bores to the pressure chambers provide supply and discharge of hydraulic medium to and from the pressure chambers, according to the position of said chambers and therewith the position of the plungers which are determined by the present position of the main shaft.
In principle two identical aggregates, as described hereinabove, may be used as a hydraulic regulating system for converting the number of revolutions/torque of an ingoing shaft into a variable number of revolutions/torque of an outgoing shaft. The ingoing shaft drives a pump as described above. The flowing hydraulic medium drives an identical aggregate which works as a driving aggregate and drives an outgoing shaft. The quantity of medium supplied determines the number of revolutions of the driving shaft; the pressure determines the torque. The two units may be combined to form one aggregate, if desired. Two mirror-symmetric aggregates may be combined into one unit, if desired.
Such a combination has a bad efficiency, especially because of flow losses of the medium. The combination of hydropump and hydromotor is applied amongst others in test-beds for transmission means. Usually they are combined into one unit with a rotatable, adjustable passage for a hydraulic medium.
A similar device is known from the British Pat. No. 135 799. According to this patent there is a second set of cylindrical bores next to a first set in the widened part of the ingoing shaft, substantially parallel to the centre line of this shaft. In the bores of this second set controlling valves are provided which are loaded on one side by a spring and on the other side by the hydraulic medium. Dependent on the displacement of these control valves the plungers can reciprocate freely or not in the corresponding bores. In this way a coupling is established or not between the ingoing and outgoing shaft. This known device serves solely as a coupling between both shafts, which coupling can be disengaged.